1. Field of the Invention
The present invention relates to reflectors constituted by laminating silver on polymer films and lamp reflectors using the reflectors and, more particularly, to a reflector having a multi-layer structure primarily constituted by silver which is excellent in light resistance and wet heat durability, and a lamp reflector using the reflector.
2. Description of the Related Art
Heretofore, an aluminum material having a high reflectance, such as an aluminum plate having a mirror-finished surface, an aluminum deposited sheet or the like, has been used as a reflector for a fluorescent lamp or an incandescent lamp. In recent years, the reflector which uses silver having a higher reflectance than aluminum in a visible light region as a reflective layer has been used mainly as a lamp reflector for a backlight of a liquid crystal display device, as well as a reflection umbrella for the fluorescent lamp and the like.
A so-called silver reflective board having a structure of PET (polyethylene terephthalate)/silver thin film layer/adhesive layer/aluminum plate or a so-called silver reflective sheet having a structure of PET/silver thin film layer/white coating/adhesive layer/aluminum deposition layer/polymer film/white coating is subjected to a predetermined processing such as folding processing or the like to be used in such reflectors as described above.
However, there has been a problem in silver that discoloration due to sulfuration and oxidation thereof in an atmosphere, and deterioration of reflectance accompanied therewith occur, as compared with aluminum. To solve the problem, there has been developed a method in which such sulfuration and oxidation of silver caused by being exposed to the atmosphere are prevented by using PET, which is a transparent polymer film, as a protective layer of silver to maintain a high reflectance (Japanese Unexamined Patent Publication JP-A 5-177758 (1993) and JP-A 9-150482 (1997), etc.) Take, for example, reliability of the silver reflective plate. Even in a high temperature (80° C.), neither blackening caused by sulfuration and the like, nor deterioration of reflectance is observed. However, in a high temperature of 80° C., silver is discolored into purple and the reflectance is rapidly deteriorated in a time period of from several hundred to several thousand hours. Further, there is a problem that, in a wet heat resistance test (60° C., 90% relative humidity), a multiplicity of white dots are generated and the reflectance is deteriorated.
Furthermore, there is a problem that, though high luminance can be obtained when the silver reflector is used as a lamp reflector for a sidelight-type backlight in a liquid crystal display device, as the luminance is increased, a luminescent line is generated to degrade a representation quality as a display.